1. Field of the Invention
The present invention relates to a method for manufacturing an electric capacitance type acceleration sensor in which a silicon substrate is used.
2. Description of the Related Art
An electric capacitance type acceleration sensor is a sensor for detecting an acceleration as a hollow layer (hereafter, referred to as a “gap”) between an electrode formed on a fixed substrate (hereafter, referred to as a “fixed electrode” and an electrode formed on a substrate with flexibility (hereafter, referred to as a “movable electrode” changes in response to the acceleration.
The sensor comprises a flexible substrate comprising a weight part for sensing the acceleration, a beam part with flexibility and a supporting part for supporting the weight part through the beam part and comprises a fixed substrate with recess part arranged to cover the weight part on the upper surface of the flexible substrate. The fixed substrate and the flexible substrate are joined to each other at the supporting part of the flexible substrate. The fixed electrode is formed on the plane on the recess part of the fixed substrate opposing to the weight part of the fixed electrode. The movable electrode is formed on the plane on the weight part of the flexible electrode opposing to the fixed electrode.
If a force from the outside is applied by acceleration, the gap between the movable electrode and the fixed electrode changes as the flexible substrate bows. The change of the gap causes a change of the electric capacitance between the electrodes. The acceleration can be measured by detecting the change of the electric capacitance.
In a conventional electric capacitance type acceleration sensor, the flexible substrate is formed by a silicon substrate, and the fixed substrate is formed by a borosilicate glass substrate. In addition, the silicon substrate and the borosilicate glass substrate are anodically joined to each other.
In the conventional electric capacitance type acceleration sensor, however, although the flexible substrate formed by the silicon substrate can be manufactured in a semiconductor manufacturing line, the fixed substrate formed by the borosilicate glass substrate cannot be formed in the same. So the fixed substrate needs to be manufactured in another manufacturing line since the silicon substrate and the like are to be contaminated by impurities from the glass in processing the glass and joining the fixed electrode anodically. Therefore, the cost of equipment becomes high due to the another manufacturing line conventionally.
Also, since the gap is conventionally formed in the early stage, the gap becomes damaged in some cases with a mechanical shock, a stress in forming a film, and so on. This lowers the yield of product.